The Intestinal Bacterial Community over Seasons and Its Relationship with Physiological Status of Yesso Scallop Patinopecten Yessoensis.

Emerging evidence indicates that the intestinal bacterial communities associated with eukaryotes play critical roles in the physiological activities and health of their hosts. Yesso scallop Patinopecten yessoensis, one of the cold-water aquaculture species in the North Yellow Sea of China, has suffered from massive mortality in recent years. In the present study, P. yessoensis were collected from Zhangzi Island, Dalian from March 2021 to January 2022 to investigate the intestinal bacterial community and physiological indices. 16S rRNA gene sequencing data revealed that the diversity of intestinal bacteria changed significantly over seasons, with the highest Chao1 (237.42) and Shannon (6.13) indices detected in January and the lowest Chao1 (115.44) and Shannon (2.73) indices detected in July. Tenericutes, Proteobacteria and Firmicutes were dominant phyla in the intestinal bacteria of P. yessoensis, among which Firmicutes and Proteobacteria significantly enriched in August and January, respectively. Mycoplasma was the most abundant genus during the sampling period, which exhibited the highest abundance in October (75.26%) and lowest abundance in August (13.15%). The functional profiles of intestinal bacteria also exhibited seasonal variation, with the pathways related to pentose phosphate and deoxyribonucleotides biosynthesis enriched in August while the glycogen biosynthesis pathway enriched in October. Redundancy analysis showed that seawater pH, dissolved inorganic nitrogen and silicate were major environmental factors driving the temporal succession of scallop intestinal bacteria. Correlation clustering analysis suggested that the relative abundances of Endozoicomonas and Vibrio in the intestine were positively correlated with superoxide dismutase activity in hepatopancreas while negatively correlated with malondialdehyde content in hepatopancreas and glycogen content in adductor muscle. All the results revealed that the intestine harbored a lower bacterial diversity and a higher abundance of Vibrio in August, compared to January, which were closely related to the oxidative stress status of scallop in summer. These findings will advance our understanding of the relationship between seasonal alteration in the intestinal bacteria and the physiological status of scallops.